Wilson.] 470 t'^e'^- 2°' 
tlio t'onnntidii of the ])olar bodies, and tlie cleava<j;^e-ain]>hiaster is 
solely derived from or formed under the influenee of the si)erm- 
archoplasm as described by Vejdovsky in Rhynchelmis, by Boveri 
in Ascaris, and by F'ick in the Axolotl. The sperm- archoplasm, 
moreover, is derived from the middle-piece of the spermatozoon ; 
not, as Fol describes, from its tip. Identical conclusions have 
been reached at the same time by A. P. Mathews in the case of 
Ai-bacia and Asterias. 
The history of the archoj)lasm has been followed out in great 
detail. The s])ermatozoon enters the egg point first, and the 
vitelline membrane, foi-med immediately afterwards, carries out 
with it the tail of the s])ermatozoon so that only the nucleus 
and the middle-piece enter the egg. Immediately upon its 
entrance the lance-shaped head of the spermatozoon rotates 
through an angle of about 180 degrees so that the base is finally 
turned inward. During this rotation the beginning of the sperm- 
aster becomes evident as a granular substance Ij^ng at the base of 
the spermatozoon and extending thence outward to the perii)her_y 
of the egg as a funnel-shaped mass. From that portion of this 
mass that lies nearest the sperm-head astral rays are developed, 
extending outward into the cytoplasm of the ovum and becoming 
continuous with its reticulum. A careful observation of the 
siiccessive stages of the rotation leaves not the least room for 
doubt that the sperm-aster is developed from, or under the 
influence of, a substance contained in the middle-piece — an 
observation entirely opposed to the statements of Fol upon this 
point. 
Preceded by the aster the male pro-nucleus now moves rapidly 
toward the egg-nucleus which advances through the vitellus to 
meet it. The first contact with the egg-nucleus is effected by 
means of the aster; and this is followed by a contact of the two 
nuclei. The sperm-nucleus now flattens down against the egg- 
nu(!leus, becomes lens-shaped, and assumes a reticular structure, 
and the two finally fuse completely, thus giving rise to a true 
segmentation-nucleus in which every trace of the distinction 
between paternal and maternal chromatin disapi)ears. Tlie 
central body of the aster meanwhile flattens against the nuclear 
mcTubrane, extends itself like a cap around the nucleus, and 
